Shelf



FIG. 1 is a top, front, right side perspective view of a shelf of the new design;

FIG. 2 is a front elevation view of thereof;

FIG. 3 is a rear elevation view thereof;

FIG. 4 is a right side elevation view thereof;

FIG. 5 is a left side elevation view thereof;

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom plan view thereof.

The broken lines in the figures show portions of the shelf which form no part of the claimed design. Additional broken lines show environment and form no part of the claimed design. Broken lines shown in dash-dot format show cutouts which form no part of the claimed design. 

CLAIM The ornamental design for a shelf, as shown and described. 